The nuclear envelope is a barrier comprised of outer and inner membranes that separate the cytoplasm from the nucleoplasm. The two membranes have different physical characteristics and protein compositions. The processes governing the stability of inner nuclear membrane (INM) proteins are not well characterized. In Saccharomyces cerevisiae the INM Asi1/3 complex, principally composed of integral membrane proteins Asi1 and Asi3, is an E3 ubiquitin ligase. In addition to its well-documented function in ER-associated degradation, the Doa10 E3 ubiquitin ligase complex partially localizes to the INM. The Asi1/3 and Doa10 complexes define independent INM-associated degradation (INMAD) pathways that target discrete sets of nuclear substrates for proteasomal degradation. Here we report that Asi1 exhibits rapid turnover (t1/2≤30 min). Its turnover depends on ubiquitin-mediated degradation by nuclear-localized proteasomes, exhibiting a clear requirement for the E2 ubiquitin-conjugating enzyme Ubc7, Cue1, and the AAA ATPase Cdc48 and co-factor Ubx1. Asi1 turnover occurs largely independent of the Asi1/3 or Doa10 complexes, indicating that it is subject to quality control at the INM in a manner distinct from the characterized INMAD pathways.s
- Received March 15, 2016.
- Accepted August 18, 2016.
- © 2016. Published by The Company of Biologists Ltd